Imaging lens and imaging apparatus

ABSTRACT

The imaging lens consists essentially of a negative first lens having a meniscus shape with a convex surface toward the object side; a negative second lens, a positive third lens; and a positive lens. When the focal length of the entire system is f, a half angle of view is ω, and the distance from the object-side surface of the first lens to the imaging plane along the optical axis is L, conditional formula (1) below is satisfied: 
       0.78&lt;2* f *tan(ω/2)/ L +0.005*ω&lt;1.00  (1).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to JapanesePatent Application No. 2014-048378, filed Mar. 12, 2014. The aboveapplication(s) is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The preset invention relates to an imaging lens and an imagingapparatus, and more particularly to an imaging lens suitable for use ina vehicle mounted camera, a surveillance camera, and the like thatutilize an image sensor, such as CCD's (Charge Coupled Device), CMOS's(Complementary Metal Oxide Semiconductor), and the like as well as to animaging apparatus equipped with this imaging lens.

2. Description of the Related Art

In recent years, image sensors such as CCD's, CMOS's, and the like haveachieved significant miniaturization and increased numbers of pixels.Therefore, there is demand for bodies of imaging devices and imaginglenses mounted thereon to be miniaturized and reduced in weight as well.Meanwhile, there is demand for the imaging lenses for use in a vehiclemounted camera, a surveillance camera, and the like to have high weatherresistance, wide angles of view which enable a satisfactory visual fieldover a wide range to be secured, and high optical performance.

Examples of the imaging lenses in the aforementioned field include theimaging lenses disclosed in Patent Documents 1 through 8 (JapaneseUnexamined Patent Publication No. 2011-232418, Japanese UnexaminedPatent Publication No. 2011-215443, Japanese Unexamined PatentPublication No. 2011-158868, Japanese Unexamined Patent Publication No.2011-158508, Japanese Unexamined Patent Publication No. 2011-138083,Japanese Unexamined Patent Publication No. 2010-276752, JapaneseUnexamined Patent Publication No. 2009-003343, and Japanese UnexaminedPatent Publication No. 2005-227426). Patent Documents 1 through 8disclose the imaging lenses of a four-lens configuration in whichaspherical surface lenses are included.

SUMMARY OF THE INVENTION

In recent years, demand for a wider angle of view has been increasing inthe fields of vehicle mounted cameras, surveillance cameras, and thelike. For example, a full angle of view which exceeds 180 degree isdesired. Further, accompanying miniaturization and increased numbers ofpixels of recent image sensors, there is demand for imaging lenses tohave high resolution and have high optical performance such thatfavorable images can be obtained up to a wide range of an imagingregion. However, it was difficult for conventional lens systems toachieve a wider angle of view and high optical performance at the sametime to a degree that meets the recent demand while being configured atlow cost and in small sizes.

The present invention has been developed in view of the foregoingcircumstances. It is the object of the present invention is to providean imaging lens that is capable of achieving a wider angle of view andhigh optical performance while being compact and low cost. It is alsothe object of the present invention is to provide an imaging apparatusequipped with this imaging lens.

An imaging lens of the present invention consists essentially of:

a negative first lens having a meniscus shape with a convex surfacetoward the object side;

a negative second lens, a point along the optical axis at the image-sidesurface of which is more toward the object side than points on both endsof the effective diameter of the image-side surface;

a positive third lens;

an aperture stop; and

a positive fourth lens in this order from the object side, wherein

conditional formula (1) below is satisfied:

0.78<2*f*tan(ω/2)/L+0.005*ω<1.00  (1),

wheref: the focal length of the entire systemω: a half angle of viewL: the distance from the object-side surface of the first lens to theimaging plane along the optical axis (back focus corresponds to an airconverted length).

The imaging lens of the present invention may include lensessubstantially without power; optical elements other than lenses such asstops, cover glasses, and the like; lens flanges; lens barrels; imagesensors; and mechanical components such as image stabilizationmechanisms, in addition to the first lens through the fourth lens.

Further, in the present invention, surface shapes of lenses, such as aconvex surface, a concave surface, a planar surface, biconcave,meniscus, biconvex, plano-convex, plano-concave, and the like; and signsof the refractive powers of lenses, such as positive and negative,should be considered in a paraxial region if aspheric surfaces areincluded therein, unless otherwise noted. Moreover, in the presentinvention, the sign of the radius of curvature is positive in the casethat a surface shape is convex on the object side, and negative in thecase that the surface shape is convex on the image side.

It is preferable for the imaging lens of the present invention tosatisfy conditional formulas (2) through (10). Note that the imaginglens of the present invention may preferably have a configuration, inwhich any one of conditional formulas (2) through (10) below issatisfied or may have a configuration in which an arbitrary combinationof two or more of the conditional formulas are satisfied. Alternatively,conditional formulas (1-1), (4-1) through (6-1) below may be satisfied.

0.13<f3/L<0.24  (2)

0.19<f4/L<0.25  (3)

3.2<d2/d4<20.0  (4)

0.31<f/f34<1.0  (5)

0.1<d6/f<0.7  (6)

vd1>40  (7)

vd2>50  (8)

vd3<40  (9)

vd4>50  (10)

0.80<2*f*tan(ω/2)/L+0.005*ω<1.00  (1-1)

4.0<d2/d4<20.0  (4-1)

0.35<f/f34<0.58  (5-1)

0.1<d6/f<0.6  (6-1),

wheref3: the focal length of the third lens,f4: the focal length of the fourth lens,L: the distance from the object-side surface of the first lens to theimaging plane along the optical axis (the back focus corresponds to anair converted length),d2: the distance between the first lens and the second lens along theoptical axis,d4: the distance between the second lens and the third lens along theoptical axis,f34: the combined focal length of the third lens and the fourth lens,f: the focal length of the entire system,d6: the distance between the third lens and the fourth lens along theoptical axis,vd1: the Abbe number with respect to the d-line of the material of thefirst lens,vd2: the Abbe number with respect to the d-line of the material of thesecond lens,vd3: the Abbe number with respect to the d-line of the material of thethird lens, andvd4: the Abbe number with respect to the d-line of the material of thefourth lens.

An imaging apparatus of the present invention is equipped with theimaging lens of the present invention described above.

According to the first imaging lens of the present invention, a shapeand power of each lens are suitably set in a lens system constituted bythe minimum number of lenses, i.e., four lenses, and conditional formula(1) is satisfied. This realizes an imaging lens having a sufficient wideangle of view and high optical performance while being configured at lowcost and in a small size.

According to the imaging apparatus of the present invention, the imagingapparatus is equipped with the imaging. This enables the imagingapparatus to be configured at low cost and in a small size, to performphotography at a wide angle of view, and to obtain high-quality images.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 1 of the present invention.

FIG. 2 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 2 of the present invention.

FIG. 3 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 3 of the present invention.

FIG. 4 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 4 of the present invention.

FIG. 5 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 5 of the present invention.

FIG. 6 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 6 of the present invention.

FIG. 7 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 7 of the present invention.

FIG. 8 is a cross-sectional view illustrating a lens configuration andoptical paths of an imaging lens of Example 8 of the present invention.

FIG. 9 illustrates the respective aberration diagrams of the imaginglens of Example 1 of the present invention.

FIG. 10 illustrates the respective aberration diagrams of the imaginglens of Example 2 of the present invention.

FIG. 11 illustrates the respective aberration diagrams of the imaginglens of Example 3 of the present invention.

FIG. 12 illustrates the respective aberration diagrams of the imaginglens of Example 4 of the present invention.

FIG. 13 illustrates the respective aberration diagrams of the imaginglens of Example 5 of the present invention.

FIG. 14 illustrates the respective aberration diagrams of the imaginglens of Example 6 of the present invention.

FIG. 15 illustrates the respective aberration diagrams of the imaginglens of Example 7 of the present invention.

FIG. 16 illustrates the respective aberration diagrams of the imaginglens of Example 8 of the present invention.

FIG. 17 is a view for explaining an arrangement of a vehicle mountedimaging apparatus according to the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. FIGS. 1 through 8are cross-sectional views illustrating examples of configuration of theimaging lenses according to the embodiments of the present invention,which respectively correspond to the imaging lenses of Example 1 through8 to be described later. The basic configurations illustrated in FIGS. 1through 8 are all the same, and the manners in which the configurationsare illustrated are also the same. Therefore, the imaging lensesaccording to the embodiments of the present invention will be describedmainly with reference to FIG. 1.

The imaging lens according to the embodiment of the present invention isa lens system of a four-lens configuration in which a first lens L1, asecond lens L2, and a third lens L3; and a fourth lens L4 are arrangedin this order from the object side along the optical axis Z. An aperturestop St is disposed between the third lens L3 and the fourth lens L4.The size of the imaging lens can be reduced in the radial direction bydisposing the aperture stop St between the third lens L3 and the fourthlens L4.

Note that in FIG. 1, the left side is the object side and the right sideis the image side. The aperture stop St shown in FIG. 1 does notnecessarily represent the size or shape thereof, but represents theposition thereof on the optical axis. Symbol Ri (i=1, 2, 3, . . . ) inFIG. 1 shows the radius of curvature of each lens surface, and symbol Di(i=1, 2, 3, . . . ) shows the distance between surfaces. FIG. 1 alsoillustrates axial rays 2 from an object point at an infinite distanceand off-axis rays 3 having the maximum angle of view.

FIG. 1 shows an image sensor 5 disposed on the imaging plane Sim of theimaging lens, taking the case of applying the imaging lens to an imagingapparatus into consideration. Further, when the imaging lens is appliedto the imaging apparatus, it is preferable for a cover glass, a low-passfilter, an infrared cut filter, or the like to be provided according tothe configurations of a camera on which the lens is mounted. FIG. 1illustrates an example in which a plane parallel optical member PP thatpresumes such components is provided between the fifth lens L5 and theimage sensor 5 (the imaging plane Sim).

The first lens L1 is configured to be a meniscus lens having a negativepower with a convex surface toward the object side. Configuring thefirst lens L1 to have a negative power and to be a meniscus lens with aconvex surface toward the object side in such a manner is advantageousfrom the viewpoint of widening the angle of view such that the angle ofview exceeds 180 degree and of correcting distortion. The first lens L1is assumed to be exposed to wind, rain, and cleansing solvents becausethe first lens L1 is disposed on the most-object side. However, there isan advantage that dirt, dust, moisture, and the like of concern undersuch conditions are not likely to remain on the object-side surface ofthe first lens L1 because the surface is convex.

Further, the second lens L2, the third lens L3, and the fourth lens L4are configured to have a negative power, a positive power, and apositive power respectively.

The second lens L2 is configured to have a shape in which a point alongthe optical axis at the image-side surface is more toward the objectside than points on both ends of the effective diameter of theimage-side surface. The expression “a point along the optical axis atthe image-side surface is more toward the object side than points onboth ends of the effective diameter of the image-side surface” meansthat a point along the optical axis should be more toward the objectside than points on both ends of the effective diameter of theimage-side surface although the image-side surface of the second lens L2may be of a shape with a convex surface toward the object side or may beof a shape with a concave surface toward the object side in the paraxialregion. Configuring the image-side surface of the second lens L2 to havesuch a shape enables the angles at which the peripheral rays enter alens or optical elements disposed after the third lens L3 to beappropriately reduced, resulting in balancing of aberration between thecenter and the periphery being facilitated.

Configuring the third lens L3 to have a positive power facilitatescorrection of distortion and lateral chromatic aberration.

Further, configuring the fourth lens L4 having a positive power to bedisposed on the back of the stop St enables the third lens L3 and thefourth lens L4 to share a positive refractive power, thereby suppressingthe occurrence of spherical aberration while maintaining a powerarrangement of a retro-focus type.

The imaging lens of the present embodiment is configured to satisfyconditional formula (1) below:

0.78<2*f*tan(ω/2)/L+0.005*ω<1.00  (1),

wheref: the focal length of the entire systemω: a half angle of viewL: the distance from the object-side surface of the first lens to theimaging plane along the optical axis (the back focus corresponds to anair converted length).

Satisfying the upper limit defined by conditional formula (1) enablesthe thinnest part of lens members which constitute the imaging lensaccording to the present embodiment to be prevented from becoming toothin. Accordingly, it is possible to secure sufficient accuracy andstrength. Further, it is also possible to provide sufficient roombetween the adjacent lenses so that assembly properties are improved,enabling cost reduction to be achieved. Moreover, the distance from therear end of the lens to the imaging plane can be secured, andappropriate arrangement of the lenses will be facilitated accordingly.Further, it is possible to make the power of each lens which constitutesthe imaging lens according to the present embodiment sufficientlystrong. Accordingly, chromatic aberration, field curvature, anddistortion can be favorably corrected. Satisfying the lower limitdefined by conditional formula (1) enables the lens system to beminiaturized so that the imaging apparatus equipped with the imaginglens according to the present embodiment can be miniaturized. Further,the imaging apparatus can be housed in the limited space and costreduction can be achieved.

A power and shape of each lens of the first lens L1 through the fourthlens L4 are suitably set in the imaging lens of the present embodiment,and conditional formula (1) is satisfied as described above. Thisenables the lens system to consist essentially of a small number oflenses, have a short total length, and be manufactured in a small sizeand at low cost. Furthermore, in the lens system, sufficiently wideangle of view can be achieved and various aberrations includingspherical aberration, field curvature, and distortion can be favorablycorrected. Further, according to the imaging lens of the presentembodiment, high resolution can be obtained over a wide range of theimaging area. Accordingly, the imaging lens of the represent embodimentcan be compatible with the recent image sensors in which the number ofpixels has been increased.

It is preferable for the imaging lens according to the presentembodiment to further have configurations described below. Note thatpreferably, the imaging lens of the present invention may have aconfiguration in which any one of conditional formulas below issatisfied or may have a configuration in which an arbitrary combinationof two or more of the conditional formulas are satisfied.

In the imaging lens of the present embodiment, it is preferable for atleast one surface of each of the second lens L2, the third lens L3, andthe fourth lens L4 to have an aspherical surface shape. Configuring atleast one surface of each of the second lens L2, the third lens L3, andthe fourth lens L4 to have an aspherical surface shape enables highresolution to be obtained while shortening the total length in thedirection of the optical axis of the optical system. Further, thisenables various aberrations such as spherical aberration, fieldcurvature, distortion, and the like to be corrected favorably with asmall number of lenses. In addition, it is preferable for both surfacesof each of the second lens L2, the third lens L3, and the fourth lens L4to have aspherical surface shapes to perform more preferable aberrationcorrection.

It is preferable for the second lens L2 to have a biconcave shape. Thisis advantageous from the viewpoint of securing back focus because agreat negative refractive power can be imparted to the second lens L2without decreasing the absolute values of the radii of curvature of theobject-side surface and the image-side surface of the second lens L2.

It is preferable for the object-side surface of the third lens L3 to beof a convex shape. This enables longitudinal chromatic aberration andlateral chromatic aberration to be corrected while suppressing theoccurrence of astigmatism.

The third lens L3 may be of a biconvex shape. This configuration isadvantageous from the viewpoint of correcting distortion and lateralchromatic aberration. In this case, increasing the radius of curvatureof the image-side surface of the third lens L3 enables longitudinalchromatic aberration, lateral chromatic aberration, and distortion to becorrected while suppressing the occurrence of astigmatism.

The third lens L3 may be of a positive meniscus shape with a convexsurface toward the object side. This enables longitudinal chromaticaberration, lateral chromatic aberration, and distortion to be correctedwhile suppressing the occurrence of astigmatism.

It is preferable for the fourth lens L4 to be of a biconvex shape. Thisis advantageous from the viewpoint of correcting distortion and lateralchromatic aberration. In this case, increasing the radius of curvatureof the object-side surface of the fourth lens L4 enables longitudinalchromatic aberration, lateral chromatic aberration, and distortion to becorrected while suppressing the occurrence of astigmatism.

The fourth lens L4 may have a positive meniscus shape with a convexsurface toward the image side. This enables longitudinal chromaticaberration, lateral chromatic aberration, and distortion to be correctedwhile suppressing the occurrence of astigmatism.

It is preferable for the imaging lens according to the presentembodiment to satisfy conditional formulas (2) through (10) below:

0.13<f3/L<0.24  (2)

0.19<f4/L<0.25  (3)

3.2<d2/d4<20.0  (4)

0.31<f/f34<1.0  (5)

0.1<d6/f<0.7  (6)

vd1>40  (7)

vd2>50  (8)

vd3<40  (9)

vd4>50  (10),

wheref3: the focal length of the third lens,f4: the focal length of the fourth lens,L: the distance from the object-side surface of the first lens to theimaging plane along the optical axis (the back focus corresponds to anair converted length),d2: the distance between the first lens and the second lens along theoptical axis,d4: the distance between the second lens and the third lens along theoptical axis,f34: the combined focal length of the third lens and the fourth lens,f: the focal length of the entire system,d6: the distance between the third lens and the fourth lens along theoptical axis,vd1: the Abbe number with respect to the d-line of the material of thefirst lens,vd2: the Abbe number with respect to the d-line of the material of thesecond lens,vd3: the Abbe number with respect to the d-line of the material of thethird lens, andvd4: the Abbe number with respect to the d-line of the material of thefourth lens.

Satisfying the upper limit defined by conditional formula (2) enableslateral chromatic aberration to be corrected. Satisfying the lower limitdefined by conditional formula (2) enables the power of the third lensL3 to be prevented from increasing and enables the size of the thirdlens L3 to be reduced in the direction of the optical axis. Thisfacilitates miniaturization of the lens and eliminates the need for highaccuracy in components, resulting in manufacturing being facilitated.

Satisfying the upper limit defined by conditional formula (3) preventsthe angles at which light rays enter the imaging plane at the peripheralportions thereof from increasing excessively. Accordingly, it becomespossible to easily take in a practically necessary amount of light.Satisfying the lower limit defined by conditional formula (3) preventsthe power of the fourth lens L4 from increasing excessively and enablesthe size of the fourth lens L4 to be reduced in the direction of theoptical axis. This facilitates miniaturization of the lens andeliminates the need for high accuracy in components, resulting inmanufacturing being facilitated.

Satisfying the upper limit defined by conditional formula (4) preventsthe distance between the second lens L2 and the third lens L3 fromdecreasing excessively and facilitates elimination of stray light.Further, when the distance between the second lens 2 and the third lensL3 is set appropriately, the distance between the first lens L1 and thesecond lens L2 will be prevented from increasing excessively andminiaturization of the lens will be facilitated. Satisfying the lowerlimit defined by conditional formula (4) prevents the distance betweenthe second lens L2 and the third lens L3 from increasing excessively andfacilitates miniaturization. Further, when the distance between thesecond lens 2 and the third lens L3 is set appropriately, the first lensL1 and the second lens L2 will be prevented from approaching each otherexcessively and the surface of the second lens L2, which is on the sideof the first lens L1, will be prevented from being a shape thatprotrudes excessively toward the side of the first lens L1. This alsoprevents the surface of the second lens L2, which is on the side of thethird lens L3, from being a shape that protrudes excessively toward theside of the first lens L1.

Satisfying the upper limit defined by conditional formula (5)facilitates favorable correction of spherical aberration. Further,securing of back focus will also be facilitated. Satisfying the lowerlimit defined by conditional formula (5) facilitates correction oflateral chromatic aberration while favorably maintaining fieldcurvature.

Satisfying the upper limit defined by conditional formula (6)facilitates miniaturization of the lens. Satisfying the lower limitdefined by conditional formula (6) prevents the third lens L3 and thefourth lens L4 from approaching each other excessively. This eliminateslimitations on the shapes of the third lens L3 and the fourth lens L4when the third lens L3 and the fourth lens L4 are to be arrangedappropriately, which improves the workability of the third lens L3 andthe fourth lens L4.

Satisfying conditional formulas (7) through (10) enable longitudinalchromatic aberration and lateral chromatic aberration to be balanced.

Further, it is preferable for conditional formulas (1-1), (4-1) through(6-1) to be satisfied. Satisfying conditional formulas (1-1), (4-1)through (6-1) enables the advantageous effects similar to those obtainedby satisfying conditional formulas (1), (4) through (6) to be obtainedor enhanced further.

0.80<2*f*tan(ω/2)/L+0.005*ω<1.00  (1-1)

4.0<d2/d4<20.0  (4-1)

0.35<f/f34<0.58  (5-1)

0.1<d6/f<0.6  (6-1)

In the imaging lens of the present invention, it is preferable for thefull angle of view to be greater than 200 degrees. The full angle viewis twice as great as the angle formed by a chief ray of the off-axisrays 3 at the maximum angle of view and the optical axis Z. Configuringthe lens system to have a wide angle of view with a full angle of viewgreater than 200 degrees will enable the lens system to meet recentdemands for wider angles of view.

For example, when the imaging lens is used in severe environments asvehicle mounted cameras, surveillance cameras, and the like, there isdemand for the first lens L1 disposed on the most-object side to be madeof a material which is resistant to surface deterioration caused by windand rain, changes in temperature due to direct sunlight, and chemicalagents such as oil, a detergent, and the like, i.e., a material whichhas high water resistance, weather resistance, acid resistance, chemicalresistance, and the like. For example, it is preferable for a glasshaving class 1 of a powder method water resistance specified by JapanOptical Glass Manufactures' Association to be used. Further, there arecases in which the first lens L1 is desired to be made of a materialwhich is hard enough not to break. Configuring the material to be aglass enables the aforementioned demands to be satisfied. Alternatively,the material for the first lens L1 may be a transparent ceramic.

Note that a protection means for improving the strength, scratchresistance, and chemical resistance may be provided on the object-sidesurface of the first lens L1. In such a case, the material of the firstlens L1 may be plastic. Such protection means may be a hard coat or awater-repelling coat.

It is preferable for the materials of the second lens L2, the third lensL3, and fourth lens L4 to be plastic. In such a case, an asphericalsurface shape can be accurately manufactured and reduction in weight andcost can be achieved.

When plastics are applied for the materials, it is preferable forplastic materials which have low water absorption rates and lowbirefringence to be selected. Selecting plastic materials having lowwater absorption rates can reduce changes in performance due to waterabsorption as much as possible, and selecting plastic materials havinglow birefringence will prevent resolution from deteriorating. To satisfythese conditions, it is preferable for the materials of the second lensL2 and the fourth lens L4 to be cycloolefin-based or cyclic olefin-basedplastics, and for the material of third lens L3 to bepolycarbonate-based or polyester-based plastics.

When a plastic is applied for at least any one of the second lens L2,the third lens L3, and the fourth lens L4, a nanocomposite material inwhich particles smaller than the wavelength of light are mixed intoplastics may be used.

In the imaging lens of the present embodiment, an antireflection filmmay be applied to each lens to reduce ghost light and the like. In thiscase, for example, in the imaging lens as shown in FIG. 1, the thicknessof the antireflection film at the peripheral portion is less than thatof the center of lens at each of the image-side surface of the firstlens L1, the image-side surface of the second lens L2, and theobject-side surface of the third lens L3. This is because angles formedby tangential lines on the respective surfaces at the peripheralportions and the optical axis are small. Accordingly, an antireflectionfilm, in which reflectance of wavelength of 600 nm through 900 nm is thelowest in the vicinity of the center, is applied to one or more surfacesincluding the image-side surface of the first lens L1 among theaforementioned three surfaces. This enables reflectance to be decreasedaveragely in the whole effective diameter and ghost light to be reduced.Alternatively, a multi-layer film coating, in which the reflectance inthe range of visible light up to approximately 900 nm is suppressed, maybe applied. Alternatively, an antireflection film produced by a wetprocess, by which a film thickness can be uniformized, may be applied.

Note that if the wavelength, reflectance of which becomes the lowest inthe vicinity of the center, is shorter than 600 nm, the wavelength,reflectance of which becomes the lowest at the peripheral portion, willbecome too short. Accordingly, the reflectance at the long-wavelengthside becomes high, resulting in reddish ghosts becoming likely to occur.Meanwhile, if the wavelength, the reflectance of which becomes thelowest in the vicinity of the center, is longer than 900 nm, thewavelength, the reflectance of which becomes the lowest at the centerportion, will become too long. Accordingly, the reflectance on theshort-wavelength side will become high, resulting in images turningreddish, and bluish ghost light becoming likely to occur. Therefore, itis preferable for a multi-layer film coating, in which the reflectancein the range of visible light up to approximately 900 nm is suppressed,to be applied. Further, an antireflection film produced by a wetprocess, by which a film thickness can be easily uniformized, may beapplied. In such a manner, even when the wavelength, the reflectance ofwhich is the lowest in the vicinity of the center, is shorter than 600nm or longer than 900 nm, the usage of a multi-layer film coating, inwhich the reflectance in the range of visible light up to approximately900 nm is suppressed, can prevent images from turning reddish, andprevent bluish ghost light from occurring. Further, the usage of theantireflection film produced by a wet process, by which a film thicknesscan be uniformized, exhibits a similar advantageous effect.

Further, in the imaging lens of the present embodiment, rays which passthe outside of the effective diameters between the respective lenseswill become stray light and reach the imaging plane, resulting inturning to ghosts. Accordingly, it is preferable for a light cuttingmeans for shielding the stray light to be provided as necessary. As thislight cutting means, an opaque paint may be applied onto portions of theoutside of the effective diameters of the lenses, or an opaque plate maybe provided therein, for example. Alternatively, opaque plates may beprovided as the light cutting means on optical paths of the rays whichbecome stray light.

Note that a filter which cuts blue light from ultraviolet light or an IR(InfraRed) cutting filter which cuts infrared light may be providedbetween the lens system and the image sensor 5 according to theapplication of the imaging lens 1. A coating which has the samecharacteristics as those of the filters above may be applied onto thelens surface.

FIG. 1 shows the example in which an optical member PP that presumesvarious types of filters, and the like is disposed between the lenssystem and the image sensor 5, but these various types of filters may bedisposed between the respective lenses, instead. Alternatively, acoating, which exhibits the same effects as the various types offilters, may be applied onto the lens surfaces of any of the lensesincluded in the imaging lens.

EXAMPLES

Next, Numerical Examples of the imaging lens of the present inventionwill be described.

Example 1

An arrangement of lens groups of an imaging lens of Example 1 isillustrated in FIG. 1. As illustrated in FIG. 1, the imaging lens ofExample 1 consists of a negative first lens L1 having a meniscus shapewith a convex surface toward the object side, a second lens L2 having abiconcave shape, a third lens L3 having a biconvex shape with a convexsurface having the small absolute value of the radius of curvaturetoward the object side, an aperture stop St, and a fourth lens L4 havinga biconvex shape with a convex surface having the small absolute valueof the radius of curvature toward the image side. Both surfaces of thesecond lens L2, the third lens L3, and the fourth lens L4 areaspherical. Configuring both surfaces of the second lens L2 to beaspherical is advantageous from the viewpoint of correcting distortionand astigmatism. Configuring both surfaces of the third lens L3 and thefourth lens L4 to be aspherical is advantageous from the viewpoint ofcorrecting spherical aberration. In the third lens L3 and the fourthlens L4, longitudinal chromatic aberration, lateral chromaticaberration, and distortion can be corrected while the occurrence ofastigmatism being suppressed. This is because the image-side surface ofthe third lens L3 and the object-side surface of the fourth lens L4 havelarge radii of curvature although these lenses L3, L4 are of a biconvexshape.

Tables 1, 2, and 3 show specific lens data corresponding to aconfiguration of the imaging lens according to Example 1. Table 1, showsbasic lens data thereof, Table 2 shows data regarding specs, and Table 3shows data regarding aspherical surface coefficients. In basic lensdata, the column of Si shows the i-th (i=1, 2, 3, . . . ) surfacenumber, the value of i sequentially increasing from a surface of theconstituent element at the most object side, which is designated as 1,toward the image side. The column Ri shows the radii of curvature of thei-th surface, and the column Di shows the distances between i-thsurfaces and i+1st surfaces along the optical axis Z. Note that anoptical member PP is also shown therein. Further, the sign of the radiusof curvature is positive in the case that a surface shape has a convexsurface toward the object side, and negative in the case that a surfaceshape has a convex toward the image side. In each Example, Ri and Di inlens data (i=1, 2, 3, . . . ) respectively correspond to signs Ri and Diof the lens cross-sectional views. Further, the column Ndj shows therefractive indices of j-th (j=1, 2, 3, . . . ) lenses with respect tothe d-line (wavelength: 587.6 nm), the value of j sequentiallyincreasing from the constituent element at the most object side, whichis designated as 1, toward the image side in lens data of Table 1. Thecolumn vdj shows the Abbe numbers of j-th optical elements with respectto the d-line. Note that the lens data also shows an aperture stop St.The column of the radii of curbature of a surface corresponding to theaperture stop St indicates ∞.

In the lens data of Table 1, the mark “*” which is indicated on the leftside of surface numbers shows that the lens surfaces, the surfacenumbers of which are indicated with the mark “*”, are of an asphericalsurface shape. In the basic lens data of Table 1, numerical values ofparaxial radii of curvature are shown as the radii of curvature of theseaspherical surfaces.

Values of the paraxial focal length f′ (mm), the back focus Bf′, the Fnumber (FNo.), and the angle of view (2ω) are shown in Table 2 as dataregarding specs of the imaging lens according to Example 1.

Table 3 shows data regarding aspherical surface coefficients of theimaging lens according to Example 1. Surface numbers of the asphericalsurfaces and aspherical surface coefficients with respect to theaspherical surfaces are shown therein. Note that “E-n” (n: integer) ineach of the numerical values of the aspherical surface coefficientsmeans “×10^(−n)”. Note that the aspherical surface coefficients are thevalues of respective coefficients KA, Am (m=3, 4, 5, . . . 20) in theaspherical surface formula below:

Zd=C·h ²/{1+(1−KA·C ² ·h ²)^(1/2) }+ΣAm·h ^(m)

where,Zd: the depth of an aspheric surface (the length of a perpendicular linedrawn from a point on an aspheric surface with a height h to a planeperpendicular to the optical axis which contacts the peak of theaspheric surface)h: height (the distance from the optical axis to a lens surface)C: an inverse number of a paraxial radius of curvatureKA, Am: aspherical surface coefficients.

The aspheric surface of the imaging lens according to Example 1 isexpressed by effectively applying orders of A3 through A20 to anaspherical surface coefficient Am, based on the above aspherical surfaceformula.

The manner in which the aforementioned Tables 1 through 3 are describedis similar to Tables 4 through 24 to be described later.

In each of Tables below, degrees (°) are used as the unit of angles andmm is used as the unit of length as described above, but otherappropriate units may also be used, as optical systems are usable evenwhen they are proportionally enlarged or miniaturized.

TABLE 1 Example 1/Lens Data Si Ri Di Ndj vdj  1 11.89689 0.99999 1.7725049.60  2 3.66231 1.93319 *3 −1.13690 0.79999 1.53391 55.89 *4 3.516540.39490 *5 1.19534 1.24733 1.61399 25.53 *6 −111111.11111 0.19867  7(Stop) ∞ 0.24951 *8 54.47734 1.48544 1.53391 55.89 *9 −0.94571 1.0999910 ∞ 0.80000 1.51680 64.20 11 ∞ 0.02044

TABLE 2 Exampla 1/Specs (d-line) f′ 0.897 Bf′ 1.648 FNo. 2.98 2ω [°]213.2

TABLE 3 Example 1/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+000.0000000E+00 0.0000000E+00 A3  3.4956700E−01 6.3085482E−012.3370302E−01 −2.0959006E−02  −1.4209815E−01  6.8695991E−02 A4−9.4816870E−02 −6.3509239E−01  −3.4939383E−01  1.9082848E−011.1196132E+00 −6.5104553E−01  A5  8.7339615E−03 3.4330279E−013.6125001E−01 −1.6305363E−01  −8.2365750E+00  2.3461839E+00 A6−6.4153910E−04 4.4565802E−01 8.3245446E−02 −9.7796480E−02  2.7906418E+01−3.8698074E+00  A7 −3.0134602E−03 −7.1409003E−02  −3.6054508E−01 5.3419516E−01 −5.3407045E+01  1.8182490E+00 A8  1.4104260E−03−3.2629066E−01  2.9838695E−01 −3.2104607E−01  9.5823106E+011.0042145E+00 A9  1.2060791E−04 −7.7093304E−02  −9.0859026E−02 −7.3624993E−02  −3.1401683E+02  1.1032281E+00 A10 −4.6650058E−058.0955309E−02 3.0130733E−02 −3.3977623E−01  6.3004486E+02−1.4831769E+00  A11 −1.1474534E−05 6.3314134E−02 −2.8263261E−02 7.5994193E−02 8.8275068E+02 −4.7605255E+00  A12 −2.9888442E−06−1.0766267E−02  6.7425893E−03 7.1426502E−01 −6.8273703E+03 6.3429811E+00 A13 −1.4703615E−06 1.4543442E−02 −6.2853723E−03 −1.5481184E+00  1.1360973E+04 −1.5463236E+00  A14  8.8545972E−07−9.5767620E−03  4.1767947E−03 8.2679326E−01 −4.3418408E+03 5.5459425E−02 A15 −5.2699157E−08 −4.3525465E−03  2.7052935E−031.6234384E−01 3.9156326E+03 −6.0648490E−01  A16  3.3085215E−08−6.5667525E−03  5.1827473E−04 −3.2821160E−01  −2.8426472E+04 4.2940043E−02 A17  2.7923977E−09 1.1012235E−03 −3.3577081E−03 9.5046217E−01 1.5248920E+04 −3.5007105E−01  A18 −4.5752566E−099.7353879E−04 −3.5240463E−04  5.1715761E−01 6.7631145E+04 6.8475228E−01A19 −5.6861028E−10 1.4025077E−03 −9.1956018E−04  1.3641323E+00−9.9834577E+04  −2.4436554E−01  A20  3.3152567E−10 −3.9503873E−04 3.4082784E−04 −1.9474017E+00  4.0208425E+04 2.1741246E−04

Example 2

FIG. 2 is a view illustrating a configuration of an imaging lensaccording to Example 2 of the present invention. The imaging lensaccording to Example 2 has the configuration substantially similar tothat of the imaging lens according to Example 1. Table 4 shows basiclens data of the imaging lens of Example 2. Table 5 shows data regardingspecs of the imaging lens of Example 2. Table 6 shows data regardingaspherical surface coefficients of the imaging lens of Example 2.

TABLE 4 Example 2/Lens Data Si Ri Di Ndj νdj  1 11.44571 0.99999 1.7725049.60  2 3.30571 1.95392 *3 −1.15359 0.79999 1.53391 55.89 *4 2.416190.41828 *5 1.00501 1.23222 1.61399 25.53 *6 −111041.25284 0.16537  7(Stop) ∞ 0.23226 *8 111111.11111 1.51937 1.53391 55.89 *9 −1.074361.09999 10 ∞ 0.80000 1.51680 64.20 11 ∞ 0.02633

TABLE 5 Example 2/Specs (d-line) f′ 0.960 Bf′ 1.654 FNo. 2.98 2ω [°]214.8

TABLE 6 Example 2/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+000.0000000E+00 0.0000000E+00 A3  3.4863781E−01 6.0627201E−012.0720633E−01 −2.9337397E−02  −1.2795061E−01  7.2120982E−02 A4−9.5486863E−02 −6.3327480E−01  −3.4528103E−01  2.2349211E−011.0794335E+00 −6.6102305E−01  A5  8.7311544E−03 3.4674563E−013.7308803E−01 −1.4973934E−01  −8.2789253E+00  2.3399252E+00 A6−6.2106243E−04 4.8443466E−01 9.3557813E−02 −9.4414788E−02  2.7789575E+01−3.8741833E+00  A7 −3.0044813E−03 −7.2649774E−02  −3.5261844E−01 5.8686260E−01 −5.3413103E+01  1.8135368E+00 A8  1.4144890E−03−3.2587395E−01  3.0489759E−01 −4.9730888E−01  9.5892833E+011.0154302E+00 A9  1.2399776E−04 −7.6424363E−02  −8.7278008E−02 −3.6953338E−01  −3.1424979E+02  1.1093941E+00 A10 −4.6966498E−058.0171611E−02 3.2266209E−02 −3.9759214E−01  6.3647369E+02−1.4875812E+00  A11 −1.1518076E−05 6.1195169E−02 −2.7291171E−02 3.2910960E−02 8.9296785E+02 −4.7622139E+00  A12 −3.0755584E−06−1.3196698E−02  7.6152125E−03 8.2913173E−01 −6.8784654E+03 6.3536068E+00 A13 −1.4976114E−06 1.1230016E−02 −6.9885127E−03 −1.0790099E+00  1.1340597E+04 −1.5538288E+00  A14  8.7368362E−07−1.4277776E−02  2.5832190E−03 1.3886655E+00 −4.4232723E+03 5.4548749E−02 A15 −5.7794708E−08 −3.8988396E−03  2.7050850E−047.2651985E−01 4.3964350E+03 −6.0721221E−01  A16  2.8033877E−08−6.5582779E−03  −2.0732836E−03  6.2417134E−02 −2.8628209E+04 4.1836758E−02 A17  2.3310296E−09 1.1441228E−03 −5.7901947E−03 1.2007740E+00 1.5042853E+04 −3.5037061E−01  A18 −4.5464944E−091.0316771E−03 −2.9630930E−03  3.0666733E−01 6.8077685E+04 6.8505231E−01A19 −4.0784706E−10 1.7724107E−03 −3.3244303E−03  7.8955961E−01−1.0130373E+05  −2.4405471E−01  A20  4.8457285E−10 1.4184559E−041.2516274E−04 −2.9582912E+00  4.1353108E+04 4.0582159E−04

Example 3

FIG. 3 is a view illustrating a configuration of an imaging lensaccording to Example 3 of the present invention. The imaging lensaccording to Example 3 has the configuration substantially similar tothat of the imaging lens according to Example 1. However, the imaginglens according to Example 3 differs from that of Example 1 in that thethird lens L3 is a positive lens having a meniscus shape with a convexsurface toward the object side and the fourth lens L4 is a positive lenshaving a meniscus shape with a convex surface toward the image side. Inthe third lens L3 and the fourth lens L4, longitudinal chromaticaberration, lateral chromatic aberration, and distortion can becorrected while suppressing the occurrence of astigmatism. This isbecause the image-side surface of the third lens L3 and the object-sidesurface of the fourth lens L4 have large radii of curvature althoughthese lenses L3, L4 are of a meniscus shape.

Table 7 shows basic lens data of the imaging lens of Example 3. Table 8shows data regarding specs of the imaging lens of Example 3. Table 9shows data regarding aspherical surface coefficients of the imaging lensof Example 3.

TABLE 7 Example 3/Lens Data Si Ri Di Ndj νdj  1 11.35047 0.99999 1.7725049.60  2 3.21831 1.94333 *3 −1.16632 0.79999 1.53391 55.89 *4 2.111420.30241 *5 1.01835 1.21006 1.61399 25.53 *6 237.31571 0.19999  7 (Stop)∞ 0.17335 *8 −9577.71793 1.64978 1.53391 55.89 *9 −0.92591 1.11886 10 ∞0.80000 1.51680 64.20 11 ∞ 0.02152

TABLE 8 Example 3/Specs (d-line) f′ 0.868 Bf′ 1.668 FNo. 2.40 2ω [°]215.4

TABLE 9 Example 3/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00  0.0000000E+00  0.0000000E+00 0.0000000E+000.0000000E+00 0.0000000E+00 A3  3.5573678E−01  5.7441118E−01 1.9078973E−01 −6.3204829E−02  −8.5273995E−02  9.0945449E−02 A4−9.8879009E−02 −6.4108858E−01 −3.5514603E−01 2.7061364E−01 1.0160951E+00−6.6896055E−01  A5  8.5434361E−03  3.6565750E−01  4.0805372E−01−8.3961333E−02  −8.2002962E+00  2.3656042E+00 A6 −6.2942739E−04 5.0501293E−01  1.1101111E−01 −3.4459034E−02  2.6982034E+01−3.8731178E+00  A7 −3.0004364E−03 −4.2068844E−02 −3.3444296E−014.4492343E−01 −5.2429953E+01  1.8153104E+00 A8  1.4107556E−03−3.0383911E−01  3.2975755E−01 −5.0367222E−01  9.9776347E+011.0028488E+00 A9  1.3014496E−04 −8.1959567E−02 −1.9113262E−01−3.0024212E−01  −3.1967560E+02  1.0927255E+00 A10 −4.2665246E−05 7.4561412E−02  1.1386275E−01 −8.1283109E−01  6.3698288E+02−1.5102125E+00  A11 −1.0061814E−05  5.5926442E−02 −2.2543037E−026.5279585E−01 8.8990200E+02 −4.7205355E+00  A12 −2.9674519E−06−1.1913081E−02  7.7881464E−03 8.1509926E−01 −6.8909128E+03 6.3680184E+00 A13 −1.8651587E−06  6.9008578E−03 −3.9707058E−033.2152428E−01 1.1331167E+04 −1.5623234E+00  A14  8.2206154E−07−2.3567980E−02  1.1294664E−02 6.1362328E−01 −4.2646840E+03 5.2080785E−02 A15 −8.5087783E−08 −6.7064024E−03 −2.2092258E−03−1.1816630E+00  4.6985266E+03 −6.0964008E−01  A16  2.7757195E−08−7.7225950E−03 −3.8320614E−03 2.6406421E−02 −3.1313926E+04 3.9054894E−02 A17  2.8584750E−09  3.5901602E−04 −4.4432965E−03−6.5274863E−02  1.6453792E+04 −3.5296860E−01  A18 −4.4072373E−09−1.0716567E−03 −1.2618319E−02 1.6217070E+00 8.0833765E+04 6.8579376E−01A19 −1.6139539E−10  1.1574430E−02 −3.7919771E−03 −3.7611643E+00 −1.2486696E+05  −2.4374520E−01  A20  6.4713186E−10 −3.0530831E−03 5.4336527E−03 2.0612624E+00 5.3292684E+04 1.2921309E−03

Example 4

FIG. 4 is a view illustrating a configuration of an imaging lensaccording to Example 4 of the present invention. The imaging lensaccording to Example 4 has the configuration substantially similar tothat of the imaging lens according to Example 3. Table 10 shows basiclens data of the imaging lens of Example 4. Table 11 shows dataregarding specs of the imaging lens of Example 4. Table 12 shows dataregarding aspherical surface coefficients of the imaging lens of Example4.

TABLE 10 Example 4/Lens Data Si Ri Di Ndj νdj  1 8.69122 0.79999 1.7725049.60  2 2.60000 1.47100 *3 −1.29382 0.59999 1.53391 55.89 *4 1.095280.16899 *5 0.64484 0.77566 1.61399 25.53 *6 5.36283 0.08895  7 (Stop) ∞0.24471 *8 −104.48947 1.31713 1.53391 55.89 *9 −0.86092 1.00636 10 ∞0.80000 1 .51680 64.20 11 ∞ 0.02743

TABLE 11 Example 4/Specs (d-line) f′ 0.964 Bf′ 1.560 FNo. 2.39 2ω [°]214.6

TABLE 12 Example 4/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+0000000000E+00 0.0000000E+00 A3  3.3678094E−01 3.7562772E−01 9.2746858E−02−9.6523518E−02  −6.8525606E−02  1.1429966E−01 A4 −1.0456534E−01−7.8656495E−01  −4.4081436E−01  5.3494100E−01 7.6506056E−01−7.9610002E−01  A5  4.8663756E−03 3.4082496E−01 4.4609605E−011.6816593E−01 −7.5705313E+00  2.4919690E+00 A6 −1.1387874E−035.8780554E−01 2.6716067E−01 4.8909174E−01 2.7137613E+01 −3.8490546E+00 A7 −2.5333287E−03 8.8747256E−02 4.0296842E−02 5.1640598E−01−5.3314002E+01  1.7639180E+00 A8  1.9204339E−03 −2.5565843E−01 8.4334550E−01 −1.8808095E+00  9.5039641E+01 8.9280581E−01 A9 4.2551148E−04 −2.0225450E−01  −2.9368210E−01  −5.3934095E+00 −3.2127857E+02  1.1439932E+00 A10  2.3223552E−05 −1.6669069E−01 −9.9463012E−02  4.8372486E+00 6.9588177E+02 −1.5452580E+00  A11−3.2071177E−05 −1.2582083E−01  −7.2409292E−01  1.0449618E+017.0439570E+02 −4.5097502E+00  A12 −1.6134506E−05 −4.1474188E−02 −1.1588084E+00  1.4585309E+01 −6.6710212E+03  6.1867164E+00 A13−9.3399064E−06 −1.1504267E−01  9.2644378E−01 −2.2820012E+01 1.1458539E+04 −1.5708845E+00  A14 −2.6584438E−06 −6.0525190E−02 2.3184840E+00 −5.8609345E+01  −4.4107789E+03  4.3699714E−02 A15−1.2315275E−06 1.3017853E−01 −2.0545063E−01  −7.7400091E+01 4.8368827E+03 −6.0817829E−01  A16 −9.3913212E−07 1.7123441E−011.5579221E+00 1.2383104E+02 −3.2781589E+04  4.1537230E−02 A17−8.3810186E−07 2.3897092E−01 6.3356931E−01 9.5236132E+01 1.8133454E+04−3.4861644E−01  A18 −1.3234788E−07 8.1679612E−03 −1.5317297E+00 1.1427713E+02 7.5873223E+04 7.3217194E−01 A19  7.6611663E−083.2550548E−02 −2.9706260E+00  −4.3205179E+02  −1.1293322E+05 −2.4697513E−01  A20  2.2187045E−07 −1.8769301E−01  −2.3490604E+00 2.6212180E+02 4.5565562E+04 −1.6523938E−02 

Example 5

FIG. 5 is a view illustrating a configuration of an imaging lensaccording to Example 5 of the present invention. The imaging lensaccording to Example 5 has the configuration substantially similar tothat of the imaging lens according to Example 3. Table 13 shows basiclens data of the imaging lens of Example 5. Table 14 shows dataregarding specs of the imaging lens of Example 5. Table 15 shows dataregarding aspherical surface coefficients of the imaging lens of Example5.

TABLE 13 Example 5/Lens Data Si Ri Di Ndj νdj  1 8.35495 0.69999 1.7725049.60  2 2.60000 1.02885 *3 −1.44505 0.49999 1.53391 55.89 *4 0.981600.19977 *5 0.64320 0.75714 1.61399 25.53 *6 4.24575 0.04999  7 (Stop) ∞0.21212 *8 −10989.01099 1.49902 1.53391 55.89 *9 −0.71695 0.82313 10 ∞0.80000 −1.51680 64.20 11 ∞ 0.02211

TABLE 14 Example 5/Specs (d-line) f′ 0.870 Bf′ 1.373 FNo. 2.45 2ω [°]203.2

TABLE 15 Example 5/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00 0.0000000E+00 0.0000000E+00  0.0000000E+000.0000000E+00 0.0000000E+00 A3  3.3390104E−01 2.9108706E−011.8796383E−01 −3.8058310E−02 −9.7724782E−02  2.0490392E−01 A4−1.0979768E−01 −7.0092517E−01  −6.6418814E−01   6.0429475E−016.9530945E−01 −8.6456578E−01  A5  3.8736413E−03 3.6485031E−016.6300094E−01  1.1890645E−01 −7.4952689E+00  2.4954510E+00 A6−3.1393290E−03 5.9962537E−01 4.9120035E−01  2.6859100E−01 2.8114738E+01−3.8453926E+00  A7 −6.4607041E−04 8.6900606E−02 2.5741296E−01−4.1682230E−01 −5.4320760E+01  1.7509210E+00 A8  1.0818308E−03−3.0924611E−01  9.6185509E−01 −2.4737616E+00 9.5002416E+01 9.8601374E−01A9  3.8599376E−04 −2.4952141E−01  −5.8502873E−01   2.8871293E+01−3.2642909E+02  1.0948601E+00 A10  6.7648202E−05 8.1106573E−03−6.6516499E−01  −2.0836411E+01 7.1065428E+02 −1.5111257E+00  A11 1.2143439E−04 −3.0700779E−01  −8.8482750E−01  −3.6198878E+016.9698488E+02 −4.7029687E+00  A12 −1.2131889E−05 −4.1244400E−01 −7.2968520E−01  −6.9974863E+01 −6.7295709E+03  6.3670069E+00 A13−8.9755296E−06 −3.7068438E−01  −1.6347411E+00  −8.3236015E+011.1595576E+04 −1.5620005E+00  A14 −1.5791612E−05 −1.4392866E−02 2.1883832E+00 −1.2590666E+00 −4.4082265E+03  3.9682480E−02 A15−3.4281499E−06 1.7105550E−01 1.4567715E+00  2.8857426E+00 4.8911187E+03−6.2131970E−01  A16 −5.4635394E−07 5.6812189E−01 8.7095431E+00−1.3281877E+02 −3.3399080E+04  2.3844427E−03 A17 −4.7187594E−065.6075383E−01 7.4949943E+00  1.4220651E+03 1.7205497E+04 −4.4253754E−01 A18 −2.6305923E−06 4.0204775E−01 1.0175355E−01 −2.5771328E+038.0923781E+04 8.8280789E−01 A19 −5.7282547E−07 5.3596188E−01−9.8867380E+00  −5.5418347E+03 −1.1874589E+05  −2.8554266E−01  A20 2.2005936E−06 −1.1886862E+00  −2.4693315E+01   5.4624965E+034.7769154E+04 −2.3520963E−02 

Example 6

FIG. 6 is a view illustrating a configuration of an imaging lensaccording to Example 6 of the present invention. The imaging lensaccording to Example 6 has the configuration substantially similar tothat of the imaging lens according to Example 3. Table 16 shows basiclens data of the imaging lens of Example 6. Table 17 shows dataregarding specs of the imaging lens of Example 6. Table 18 shows dataregarding aspherical surface coefficients of the imaging lens of Example6.

TABLE 16 Example 6/Lens Data Si Ri Di Ndj νdj  1 9.60416 1.12865 1.7725049.60  2 2.60000 1.84279 *3 −1.24381 0.59999 1.53391 55.89 *4 1.017290.15000 *5 0.76840 1.12811 1.61399 25.53 *6 9298.17369 0.13761  7 (Stop)∞ 0.22273 *8 −173.69331 1.61236 1.53391 55.89 *9 −0.91526 1.37080 10 ∞0.80000 1.51680 64.20 11 ∞ 0.02525

TABLE 17 Example 6/Specs (d-line) f′ 0.897 Bf′ 1.923 FNo. 2.44 2ω [°]215.0

TABLE 18 Example 6/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+000.0000000E+00 0.0000000E+00 A3  3.4010248E−01 3.5717345E−011.1942906E−01 −1.0376670E−01  −4.8089399E−02  1.5377001E−01 A4−1.0306111E−01 −7.1248556E−01  −4.9529291E−01  3.5384739E−017.8973458E−01 −8.0715651E−01  A5  7.4867139E−03 3.5809611E−013.9751785E−01 5.2921637E−02 −7.7413889E+00  2.4579215E+00 A6−1.3392857E−03 5.9366551E−01 2.2522066E−01 −8.1247249E−02  2.7622387E+01−3.8436363E+00  A7 −2.8864402E−03 9.5266332E−02 −1.4090959E−01 3.4761383E−01 −5.2798777E+01  1.7884375E+00 A8  1.5490655E−03−1.9797731E−01  4.6834062E−01 −6.7296990E−01  9.5610812E+019.7704113E−01 A9  2.5475127E−04 −1.3718420E−01  −1.3491489E−01 −4.0209740E−01  −3.2772255E+02  1.0893018E+00 A10 −1.9386788E−051.5517618E−01 −5.7751053E−02  −8.6537136E−01  6.9739811E+02−1.5115746E+00  A11 −1.2872725E−06 −8.4128594E−02  −1.3463947E−01 6.7695118E−01 7.2772866E+02 −4.7075186E+00  A12 −1.7902868E−06−1.1231840E−01  −4.5494233E−02  1.1167748E+00 −6.6929161E+03 6.3675607E+00 A13 −1.4973753E−06 −8.3661126E−02  −1.8503788E−01 7.6702869E−01 1.1491679E+04 −1.5557889E+00  A14 −5.3245522E−07−1.3833416E−01  3.9359124E−02 1.5617873E+00 −4.5164167E+03 5.4721304E−02 A15 −5.0870445E−07 −1.0450107E−02  7.7110283E−021.9353874E+00 4.6941223E+03 −6.1052912E−01  A16 −2.9945676E−075.8789360E−02 1.2061686E−01 −3.1679493E+00  −3.2712017E+04 3.2360271E−02 A17 −1.2526217E−07 1.1019828E−01 1.2599472E−012.3902163E+00 1.8588884E+04 −3.5849326E−01  A18 −7.2098014E−086.1181762E−02 6.6458159E−02 −6.0115454E+00  7.7905791E+04 6.9288132E−01A19 −3.9532702E−08 5.4388271E−02 −4.5807396E−02  −2.7222782E+01 −1.1794492E+05  −2.3645629E−01  A20  5.3885163E−08 −9.4281034E−02 −2.0322533E−01  2.9210420E+01 4.82S8365E+04 −4.5567560E−03 

Example 7

FIG. 7 is a view illustrating a configuration of an imaging lensaccording to Example 7 of the present invention. The imaging lensaccording to Example 7 has the configuration substantially similar tothat of the imaging lens according to Example 1. Table 19 shows basiclens data of the imaging lens of Example 7. Table 20 shows dataregarding specs of the imaging lens of Example 7. Table 21 shows dataregarding aspherical surface coefficients of the imaging lens of Example7.

TABLE 19 Example 7/Lens Data Si Ri Di Ndj νdj  1 12.20879 0.999991.77250 49.60  2 3.90042 1.96286 *3 −1.12244 0.79999 1.53391 55.89 *43.88915 0.34165 *5 1.36760 1.28813 1.61399 25.53 *6 −12.04543 0.24867  7(Stop) ∞ 0.27107 *8 17.29534 1.41153 1.53391 55.89 *9 −0.95378 1.0999910 ∞ 0.80000 1.51680 64.20 11 ∞ 0.01843

TABLE 20 Example 7/Specs (d-line) f′ 0.886 Bf′ 1.646 FNo. 2.98 2ω [°]212.8

TABLE 21 Example 7/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00 0.0000000E+00 0.0000000E+00  0.0000000E+000.0000000E+00 0.0000000E+00 A3  3.4958384E−01 6.4891560E−012.4466106E−01 −2.2854221E−02 −1.4442013E−01  4.3741341E−02 A4−9.3949685E−02 −6.4450678E−01  −3.5884218E−01   1.8031623E−011.1967422E+00 −6.2647789E−01  A5  8.6063960E−03 3.3293814E−013.3653731E−01 −1.7776251E−01 −8.3341941E+00  2.3588720E+00 A6−6.6312770E−04 4.3790545E−01 7.6386477E−02 −1.1077204E−01 2.7909764E+01−3.8666008E+00  A7 −3.0200815E−03 −7.9629695E−02  −3.6591721E−01  5.0375065E−01 −5.3426072E+01  1.8157060E+00 A8  1.4088556E−03−3.2537618E−01  2.9420319E−01 −3.1766583E−01 9.5830737E+01 1.0017512E+00A9  1.2032656E−04 −7.5951683E−02  −9.2529015E−02  −6.3720742E−02−3.1404500E+02  1.1010991E+00 A10 −4.6844397E−05 8.2730770E−022.9060351E−02 −2.9504503E−01 6.3047035E+02 −1.4857391E+00  A11−1.1446180E−05 6.4655791E−02 −2.8336345E−02   2.2929453E−018.8286517E+02 −4.7626625E+00  A12 −2.9368997E−06 −9.8863212E−03 6.8004897E−03  7.7905177E−01 −6.8231665E+03  6.3363291E+00 A13−1.4639451E−06 1.5310270E−02 −5.7140364E−03  −1.4964053E+001.1364519E+04 −1.5410611E+00  A14  8.9188706E−07 −8.8542397E−03 4.6537166E−03  8.8220265E−01 −4.3406277E+03  5.9278599E−02 A15−5.0940341E−08 −3.5221831E−03  3.1272680E−03  4.7896091E−023.7681463E+03 −6.0357408E−01  A16  3.2984640E−08 −6.5532014E−03 8.2115386E−04 −3.7457689E−01 −2.8154760E+04  4.3660764E−02 A17 2.9040623E−09 1.0217784E−03 −2.8636194E−03   8.2788500E−011.5253224E+04 −3.4945551E−01  A18 −4.6135873E−09 9.3594272E−04−4.1543337E−04  −3.3035497E−01 6.7010625E+04 6.8276769E−01 A19−5.3740236E−10 1.3015759E−03 −6.5276558E−04  −4.8112157E−01−9.8946021E+04  −2.4572308E−01  A20  2.9705744E−10 −5.1495827E−04 4.7511009E−04  2.6654376E−01 3.9795273E+04 8.9865749E−04

Example 8

FIG. 8 is a view illustrating a configuration of an imaging lensaccording to Example 8 of the present invention. The imaging lensaccording to Example 8 has the configuration substantially similar tothat of the imaging lens according to Example 1. Table 22 shows basiclens data of the imaging lens of Example 8. Table 23 shows dataregarding specs of the imaging lens of Example 8. Table 24 shows dataregarding aspherical surface coefficients of the imaging lens of Example8.

TABLE 22 Example 8/Lens Data Si Ri Di Ndj νdj  1 12.22075 0.999991.77250 49.50  2 3.87304 1.96122 *3 −1.12955 0.81735 1.53391 55.89 *43.83199 0.33059 *5 1.35741 1.26858 1.61399 25.53 *6 −13.08853 0.24003  7(Stop) ∞ 0.27046 *8 19.43408 1.42209 1.53391 55.89 *9 −0.95044 1.1052410 ∞ 0.80000 1.51680 64.20 11 ∞ 0.00000

TABLE 23 Example 8/Specs (d-line) f′ 0.887 Bf′ 1.658 FNo. 2.98 2ω [°]212.2

TABLE 24 Example 8/Aspherical Surface Coefficients Surface Numbers 3 4 56 8 9 KA  0.0000000E+00 0.0000000E+00 0.0000000E+00  0.0000000E+000.0000000E+00 0.0000000E+00 A3  3.4961809E−01 6.4886146E−012.4278701E−01 −2.7024650E−02 −1.4438707E−01  4.5299636E−02 A4−9.3955832E−02 −6.4335253E−01  −3.6043136E−01   1.7904231E−011.1884831E+00 −6.2988544E−01  A5  8.6058929E−03 3.3435864E−013.3646690E−01 −1.7679784E−01 −8.3377958E+00  2.3555147E+00 A6−6.6372893E−04 4.3906755E−01 7.7508214E−02 −1.0924920E−01 2.7905611E+01−3.8675988E+00  A7 −3.0202365E−03 −7.9051806E−02  −3.6479078E−01  5.0641679E−01 −5.3428375E+01  1.8167091E+00 A8  1.4085410E−03−3.2497724E−01  2.9511089E−01 −3.1973374E−01 9.5827643E+01 1.0021735E+00A9  1.2010922E−04 −7.6115951E−02  −9.2202627E−02  −6.4096174E−02−3.1410085E+02  1.1016389E+00 A10 −4.6905869E−05 8.2462841E−022.9047442E−02 −2.9726537E−01 6.3048957E+02 −1.4854775E+00  A11−1.1534353E−05 6.4483638E−02 −2.8526376E−02   2.2681624E−018.3297493E+02 −4.7626423E+00  A12 −2.9468425E−06 −9.9816514E−03 6.5697599E−03  7.7628700E−01 −6.8232234E+03  6.3360765E+00 A13−1.4697938E−06 1.5247166E−02 −5.9391669E−03  −1.4986584E+001.1364562E+04 −1.5416094E+00  A14  8.9228586E−07 −8.8822431E−03 4.4799308E−03  8.8100458E−01 −4.3400974E+03  5.8594906E−02 A15−5.1070088E−08 −3.5317724E−03  3.0048108E−03  4.7542187E−023.7686980E+03 −6.0426260E−01  A16  3.3064609E−08 −6.5880023E−03 7.6300339E−04 −3.6557828E−01 −2.8155444E+04  4.3028250E−02 A17 2.9340272E−09 1.0150015E−03 −2.8628511E−03   8.3284667E−011.5251433E+04 −3.4991095E−01  A18 −4.5976302E−09 9.3869753E−04−3.6748838E−04  −3.2220059E−01 6.7010232E+04 6.8279041E−01 A19−5.4229340E−10 1.3031571E−03 −6.5176858E−04  −4.6797440E−01−9.8957071E+04  −2.4526599E−01  A20  3.1356630E−10 −5.1259236E−04 5.8579524E−04  2.8650370E−01 3.9808385E+04 1.1636113E−03

Further, Table 25 shows values corresponding to conditional formulas (1)through (10) of Examples 1 through 8. As can be seen from Table 25, thevalues of each of the Examples are within the numerical ranges of therespective conditional formulas (1) through (10).

TABLE 25 Expression Number Conditional Formula Example 1 Example 2Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 (1) 2 * f *tan (ω/2)/ 0.802 0.828 0.804 0.909 0.848 0.817 0.796 0.794 L + 0.005 * ω(2) f3/L 0.217 0.182 0.186 0.160 0.182 0.143 0.231 0.231 (3) f4/L 0.1960.224 0.194 0.230 0.214 0.196 0.194 0.194 (4) d2/d4 4.895 4.671 6.4268.705 5.150 12.285 5.745 5.932 (5) f/f34 0.399 0.436 0.360 0.547 0.4350.358 0.406 0.408 (6) d6/f 0.499 0.415 0.430 0.346 0.301 0.402 0.5870.575 (7) ν d1 49.60 49.60 49.60 49.60 49.60 49.60 49.60 49.60 (8) ν d255.89 55.89 55.89 55.89 55.89 55.89 55.89 55.89 (9) ν d3 25.53 25.5325.53 25.53 25.53 25.53 25.53 25.53 (10)  ν d4 55.89 55.89 55.89 55.8955.89 55.89 55.89 55.89

[Aberration Performance]

FIG. 9 shows spherical aberration, astigmatism, distortion, and lateralchromatic aberration in this order from the left side in the imaginglens according to Example 1. Distortion diagrams show the amount ofdisplacement from an ideal image height which is 2f×tan(φ/2) by usingthe focal length f of the entire system and an angle of view φ (which isa variable, 0≦φ≦ω). Each aberration diagram shows aberration withrespect to the d-line (wavelength: 587.6 nm) as the referencewavelength. Each spherical aberration diagram shows aberrations withrespect to the g-line (wavelength: 436 nm), the F-line (wavelength:481.6 nm), and the C-line (wavelength: 656.27 nm). Each lateralchromatic aberration diagram also shows aberrations with respect to theg-line, the F-line, and the C-line. FNo. in each of sphericalaberrations refers to a F number, ω in each of the other aberrationdiagrams refers to a half angle of view.

Similarly, the aberration diagrams of spherical aberration, astigmatism,distortion, and lateral chromatic aberration of each of the imaginglenses of the aforementioned Examples 2 through 8 are shown in FIGS. 10through 16. FIGS. 10 through 16 also illustrate spherical aberration,astigmatism, distortion, and lateral chromatic aberration in this orderfrom the left side.

The present invention is not limited to the embodiments and the examplesdescribed above, and various modifications are possible. For example,values, such as the radius of curvature, the distances between surfaces,the refractive indices, of each lens element, and the like are notlimited to the values in the numerical examples shown in the Tables, butmay be other values.

As can be found from the data described above, each of the imaginglenses of Examples 1 through 8 is constituted by the small number oflenses, i.e., four lenses; and miniaturization and low cost areachieved. Further, the respective imaging lenses have extremely widefull angles of view which exceed 200 degrees, e.g., 203.2 through 215.4degrees, and have high optical performance with each aberrationcorrected favorably. These imaging lenses can be suitably used forsurveillance cameras, vehicle mounted cameras for photographing imagesin the front, side, and back of an automobile, and the like.

FIG. 17 shows the aspect of an automobile 100 on which the imagingapparatus provided with the imaging lens of the present embodiment ismounted, as a usage example. In FIG. 17, the automobile 100 is providedwith an outside-vehicle camera 101 for photographing a blind angle rangeon the side surface of the passenger's side thereof, an outside-vehiclecamera 102 for photographing a blind angle range behind the automobile100, and an in-vehicle camera 103, which is provided on the back of aroom mirror, for photographing the same visual field range as thedriver's. The outside-vehicle cameras 101, 102, and the in-vehiclecamera 103 correspond to the imaging apparatus according to theembodiment of the present invention, and are provided with the imaginglens according to the present embodiment of the present invention and animaging element which converts an optical image formed by the imaginglens into an electric signal.

All the imaging lenses according to the Examples of the presentinvention have the advantageous points described above. Accordingly, theoutside-vehicle cameras 101, 102, and the in-vehicle camera 103 can bealso configured in a small size and at low costs, have wider angles ofview, and enables fine images to be obtained even in the peripheralportions of the imaging area.

The present invention has been described with reference to theEmbodiments and Examples. The present invention is not limited to theembodiments and the examples described above, and various modificationsare possible. For example, values, such as the radius of curvature, thedistances between surfaces, the refractive indices, the Abbe numbers ofeach lens element, and the like are not limited to the values in thenumerical examples shown in the Tables, but may be other values.Further, the materials of lenses are not limited to those applied in therespective numerical examples described above, but may be othermaterials.

The embodiment of the imaging apparatus was described with reference tothe Figure of an example, in which the present invention is applied to avehicle mounted camera. The present invention is not limited to thisapplication and can be applied to portable terminal cameras,surveillance cameras, and the like, for example.

What is claimed is:
 1. An imaging lens of the present invention consistsessentially of: a negative first lens having a meniscus shape with aconvex surface toward the object side; a negative second lens, a pointalong the optical axis at the image-side surface of which is more towardthe object side than points on both ends of the effective diameter ofthe image-side surface; a positive third lens; an aperture stop; and apositive fourth lens in this order from the object side, whereinconditional formula (1) below is satisfied:0.78<2*f*tan(ω/2)/L+0.005*ω<1.00  (1), where f: the focal length of theentire system, ω: a half angle of view, and L: the distance from theobject-side surface of the first lens to the imaging plane along theoptical axis (back focus corresponds to an air converted length).
 2. Theimaging lens of claim 1 that satisfies conditional formula (2) below:0.13<f3/L<0.24  (2), where f3: the focal length of the third lens, andL: the distance from the object-side surface of the first lens to theimaging plane along the optical axis (the back focus corresponds to anair converted length).
 3. The imaging lens of claim 1 that satisfiesconditional formula (3) below:0.19<f4/L<0.25  (3), where f4: the focal length of the fourth lens, andL: the distance from the object-side surface of the first lens to theimaging plane along the optical axis (the back focus corresponds to anair converted length).
 4. The imaging lens of claim 1 that satisfiesconditional formula (4) below:3.2<d2/d4<20.0  (4), where d2: the distance between the first lens andthe second lens along the optical axis, and d4: the distance between thesecond lens and the third lens along the optical axis.
 5. The imaginglens of claim 1 that satisfies conditional formula (5) below:0.31<f/f34<1.0  (5), where f34: the combined focal length of the thirdlens and the fourth lens, and f: the focal length of the entire system.6. The imaging lens of claim 1 that satisfies conditional formula (6)below:0.1<d6/f<0.7  (6), where d6: the distance between the third lens and thefourth lens along the optical axis, and f: the focal length of theentire system.
 7. The imaging lens of claim 1 that satisfies conditionalformulas (7) through (10) below:vd1>40  (7)vd2>50  (8)vd3<40  (9)vd4>50  (10), where vd1: the Abbe number with respect to the d-line ofthe material of the first lens, vd2: the Abbe number with respect to thed-line of the material of the second lens, vd3: the Abbe number withrespect to the d-line of the material of the third lens, and vd4: theAbbe number with respect to the d-line of the material of the fourthlens.
 8. The imaging lens of claim 1 that satisfies conditional formula(1-1) below:0.80<2*f*tan(ω/2)/L+0.005*ω<1.00  (1-1), where f: the focal length ofthe entire system, ω: a half angle of view, and L: the distance from theobject-side surface of the first lens to the imaging plane along theoptical axis (the back focus corresponds to an air converted length). 9.The imaging lens of claim 1 that satisfies conditional formula (4-1)below:4.0<d2/d4<20.0  (4-1), where d2: the distance between the first lens andthe second lens along the optical axis, and d4: the distance between thesecond lens and the third lens along the optical axis.
 10. The imaginglens of claim 1 that satisfies conditional formula (5-1) below:0.35<f/f34<0.58  (5-1), where f34: the combined focal length of thethird lens and the fourth lens, and f: the focal length of the entiresystem.
 11. The imaging lens of claim 1 that satisfies conditionalformula (6-1) below:0.1<d6/f<0.6  (6-1), where d6: the distance between the third lens andthe fourth lens along the optical axis, and f: the focal length of theentire system.
 12. An imaging apparatus comprising: imaging lens ofclaim 1.